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A. G. BELL 8L S. TAINTBR.

Photophonio Receiver. No. 241,909. Patented May 24, |881.

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' Photophone Receiver. No. 241.909.

Patented May 24, |881.

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UNITED STATES PATENT OEEICE,

ALEXANDER G. BELL AND SUMNEE TATNTEE, or WASHINGTON, D. c.\

PHOTOPHONIC RECEIVER.

SPECIFICATION forming part of Letters Patent No. 241,909, dated May 24, 1881.

Application filed March 24, 1881. (No model.) i

.To all whom 'it may concern:

Be it known that we, ALEXANDER GRAHAM BELL and SUMNEE TAINTER, both of Washington, in the District of Columbia, have invented a new and useful Improvement in Photophonic Receivers for the Production and Reproduction of Sound by the Action of Radiant Energy, which invention is fully set forth in the following specification.

The invention relates more particularly to the reproduction of articulate speech photophonically-thatis, by the action of radiant energy from the sun or other suitable source-but is also applicable, in whole or in part, to the production or reproduction of other sounds, to the production of electrical and other ei'ects, and to other purposes. It is intended asan improvement upon the photophone for which Letters Patent No. 235,199 were granted to Alexander Graham Bell, December 7, 1880.

The said photophone consists, generally, ot' a photophonic transmitter, by which a vibratory or undulatory beam or pencil of rays is produced,corresponding in its vibrations or undulations with the atmospheric vibrations that represent the sound to be produced or reproduced, and a photophonic receiver, by which the vibrations or undulations in the said beam or pencilof rays are converted into soundwaves, or into vibrations in an electric current that can be converted into sound-waves.

The present invention has reference to the photophonic receiver, and comprises means for converting the radiant vibrations, as the vibrations or undulations of the beam of rays may be called, into sound-waves, and alsointo electric `vibration s.

As described in the aforesaid patent, the radiant vibrations were converted into soundrate of interruption, and were loud enough to be easily heard.

We have discovered that the loudness of the sound is increased by having the illuminated or exposed side ofthe sensitive medium in contact with the air of the sound-chan. ber with which the ear-tube is connected, and y allowing the radiant beam to fall upon said medium through a plate of glass or similar material 6o which is transparent to radiant energy, but opaque or less transparent to sound-waves.

In this way the full eifect of the radiant vibrations upon the sensitive medium is obtained, and the resulting sound-waves are shut in and conveyed to the ear with approximately their full force.

We have further discovered that a dark or black color in the sensitive medium is advantageous, and that with substances in an open, 7o porous, or subdivided condition louder sounds are in general obtained than with diaphragms. The best effects are obtained with lamp-black deposited upon a surface of glass or other hard or rigid material. With a layer of this sub- `stance as the sensitive medium, articulate Y speech has been reproduced by the direct action of radiant energy upon said medium. In the experiments in which this result was obtained sunbeams were reflected from a mirror 8o of thin glass silvered, (as described in Letters Patent No. 235,496, granted to us December 1 4, 1880,) and the mirror, being thrown into vibration by the voice, causedmore orless ofthe sunbeams to fall upon the lam p-black. The latter was deposited upon the inner walls of a soundchamber havin gone sideformed of a glass plate to transmit the radiant beam, and having an ear-tube communicating with the interior, as explained above. 9o

Articulate speech has also been reproduced with areceiver containing amass of lamp-black Y in a loose pulverulent condition. A lump of lamp-black, when exposed in the sound-chamber to the action of an intermittent beam, gives 9 5 a loud sound, but inferior to that given by the same substance in the form of loose powder or a deposited layer.

Instead of smoking the walls of the soundchamber, a plate of glass, mica, or other materoo rial can be smoked and placed in said chamber so that the light falls upon the smoked surface.

The loudest sounds with the intermittent beam have been obtained by means of an open Wiregauze smoked or covered with a deposit of lamp-black. With a tubular resonator having the interior smoked a loud sound is produced when an intermittent beam having the proper rate of vibration is allowed to fall into it.

Numerous experiments have been made with various other substances. Black worsted may be mentioned as giving, with the intermittent beam, a good sound, although much inferior to lamp black. Fibrons material coated with lamp-black has also been used.

Conducting-bodies generally, in a physical condition similar to lamp-black, especially it' ot' dark or black color, yield good sound. Spongy platinum should be particularly mentioned. Other metals ormetalliccompoundsas silver, copper, black oxide of manganese, and the like-are also sensitive to radiant energy, and give out sound by the direct action ofa vibratory beam. The production of sound in this way is conceived to be due to au absorption and expulsion of the air by the vibratory medium acting, as it were, like a sponge. Thus when the energy of the radiant beam increases the particles composing the vibratory medium expand and expel the air l'roni between them, and when it decreases the reverse action takes place and the air is again absorbed. These repeated expulsions and absorptions are proportionate to the rise and fall of radiant e11- ergy, and produce corresponding condensations and raret'actions-or, in other words, soun d-waves--in the surrounding atmosphere. Heat due to the absorption of the radiant energy seems therefore to be the principal agent in producing the sound-waves.

In the photophone as described in Patent No. 235,199, above mentioned, the radiant vibrations were converted into electrical vibrations by a ditTerent material from any used for the direct production of sound -waves, the peculiar substance selenium being employed. The resistance which selenium-when properly prepared, offers to an electric current was *knownr to vary under the inuence of rays from the sun or other suitable source of radiant energy, and it was therefore employed as the medium for converting the radiant into electric vibrations. It was included in the circuit ot' a galvanic battery and placed in such position that the radiant beam fell upon it. The variations in the radiant energy due to the vibrations in the beam produced correspondin g variations in the resistance of the selenium and in the galvanic circuit of which it formed a part, and consequently in the tension of the current on said circuit, or,in other words, they produced electrical vibrations in that circuit. By the aid of cells constructed to expose a large surface ot` the selenium, and the proper preparation of the latter, an apparatus was produced so sensitive to variations in radiant energy that, with a suitable photophonic transmitter and with an ordinary hand-telephone and galvanic circuit connected with the photophonic recelvin g apparatus, articulate speech was reproduced photophonically.

We have discovered that the same medium used to produce musical notes or to reproduce speech by the direct action of the radiant vibrations can be used to convert the latterinto electric vibrations.

It' a layer of lamp-black is included in an electric circuit and is exposed to the action of a vibratory beam ot' rays from the sun or other source, variations are produced in the electric resistance ot' the lamp-black, which variations correspond to thosein the energy ol' the vibratorybeam. It' anintermittentbeain is allowed to t'all upon the lam p-blaek, electrical impulses are produced in the circuit in which thelampblack is included corresponding to the radiant impulses of the beam, and it' a telephonie receiver is also included in the circuit a musical note will he heard. Il an undnlatoryor vibratory beam from the retlecting-transinitter before mentioned, or other speakiiig-transmitter which gives to the beam vibrations similar in rate, amplitude, and quality to the soundwaves ot' articulate speech, is allowed to t'all upon the lamp-black, the electric und ulations or vibrations in the galvanic circuit will repv resent the words and sentences which produced the vibratory beam, and it' the apparatus is suiiiciently sensitive these words and sentences can be reproduced by an ordinary telephonie receiver. The use ot' selenium, which is objectionable for reasons based upon the nature ofthe substance itself, as well as upon its high price and scarcity, can therefore be dispensed with. The same objections do not apply to lamp-black.

The action of radiant energy upon the vibratory medium to produce variations in the electrical resistance ot' the latter appears to be similar to that in producing sound by direct action-that is to say, the particles are brought together or moved apart according to the increase or decrease ot' the energy ot' thc beam. They consequently furnish to the electric current a path of less or greater re` sistance.

All conductors in a physical condition similar to lamp-black have their electrical resistance affected by radiant energy. Spongy platinum is an example.

We have devised a form of cell whereby any desired extent of surface of the lam pblack can be exposed to the radiant energy without introducing undue resistance into the electric circuit.

Reference has hereinbefore been made to the cells used with selenium. These cells, the construction of which is fully described in Letters Patent Nos. 235,497 and 235,588, both dated December 14, 1880, consist, mainly, of two or more condnctin g strips, plates, or disks, placed side by side and separated by thin sheets of insulating material, which extend nearly to the edges of the plates, so as to leave a narrow IOO IIC

and shallow but long space to receive the selenium. The poles of the battery being'connected with the plates which form rtheconductors of the cell, the current flows from one to the other through the selenium, meeting but small resistance on account ofthe thinness ot' the selenium layer. In some cases the selenium was cast around metallic pins embedded in insulating material connected with the poles of the battery.

In the present invention the conductors are formed of thin strips, plates, sheets, Wires, or films xed or mounted upon an insulating backing or support with their edges opposed and near together, so as to leave one or more narrow channels to receive the sensitive medium. Cells of this character are lnnch simpler than those already patented, and they are, besides, better adapted to use in connection with lampblack. The improved cells can be made with a curved or cylindrical surface, although a dat surface would generally be preferred, and the conductors` can be made of various forms and metals.

Excellent results have been obtained with a cell having` two conductors which resemble in appearance combs with wide-spaced teeth, and which are secured to the insulatingbacking in such rela-tive position that the teeth of one comb alternate or intermesh with the teeth of the other, but are not in contact with them. The sensitive medium fills the spaces between the teeth of the two conductors, and by increasing the number and length of the teeth the surface can be increased to anydesired extent. The resistance to the electric current will, of course, depend upon the mass or area of sensitive medium, and upon the distance which separates the teeth of one comb from those ot' the other.

In order that the electric current may liow equally from the several teeth, or generally from one conductor to another, it is necessary that the spaces between their adjacent edges should be everywhere the same.

We have found that a tilm of silver deposited upon a glass plate by the methods ordinarily employed for silveriiigmirrors is possessed of great toughness, and can, with a suitable tool, be ruled or scraped off in stripes, so as to leave sharp edges lwhich appear clean and well delined, even under a microscope. As the silvered film is not affected injnriously by lamp-black, it is, from its great conductivity and the accuracy with which it can be ruled, eminently adapted to use in this invention as the conductor of the photophonic receiver. rlhe silvered film can be deposited upon a curved or flat surface, and can be scraped oft in straight, zigzag, circular, spiral, or other suitable lines. The width of the stripe or stripes removed is regulated by the scrapingtool, and the position of thelatterin operation is controlled and adjusted by mechanical means, so that the utmost exactness can be obtained.

In the cell before referred to as givingexcellent results the intermeshing combs were formed by scraping a silvered film from a ilat glass plate, as just described. This form of conductor is, however, obviously of general application, and can be employed with various metals. For example, the combs can be cut from tin-foil and pasted upon glass. Thelampblack is applied to these cells by smoking the proper surface over a flame from a coal-oil lamp or other suitable burner. The lampblack will be deposited on the conductors as well as between them; but this does notinterfere with the practical workings of the apparatus. The depth of the layer deposited may be just sutticient to render the surface sensibly opaque. The character of the result is affected by the depth and 'also by thc extent of surface exposed to the radiant energy. Although no special extent is requisite, a very large surface is not desirable, and there is a certain limitat which the best results are obtained in any case; but this limit varies with the energy of the radiant beam, the strength of the battery, and other conditions, so that no simple rule can be given. By depositing upon the silvered glass, ruled or scraped as explained, a layer which is sensibly opaque and wiping it ot'f gradually around the edges, a spot of suitable size and character can be readily obtained.

The cell is ordinarilyr sectired in position in a sound-chamber having a glass plate for the en trance of the radiant beams, and it is so placed that said beams fall upon the lamp-black. If it is desired to receive a message or signal directly, as well as through the intermediary of the electric current, the soundchamber is pro vided with one or more ear-tubes.

The lamp-black cell can be located in the main circuit in which the electrical or telephonie receiving apparatus is placed, or it can beconnected with a receiving-circuit by means of an induction coilor coils, as telephonie transmitters using a battery have been connected.

Having explained the general principles of our invention, we will now proceed to describe apparatus constructed in accordance with the same, reference being had to the accompanying drawings; which forin a part of this speciication.

Figure l is a sectional view, illustrating apparatus for transmitting speech photophoni cally without the aid of an electric eii cuit Fig. 2, a sectional view of a slightly altered form of a receiver, shown in connection with the apparatus for producing an intermittent beam; Fig. 2, a front view of one ofthe disks of the intermittent-beam apparatus; Fie'. 2b, a similar view of a wire-gauze disk used in the receiver; Figs. 3 and 4, views, in section and plan, of the lamp-black cell with internieshing combs of silver iilm Figs. 5 and 6, plan views ofother forms of the cell; Fig. 7, a view showing the cell in circuit with galvanic battery and handtelephone and the intermittent-beam appa--y ratus asthe photophonic transmitter; .and Fig.

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8, a view, partly in section, illustrating the apparatus for transmitting speech, and showing a photophonic receiver connected with a telephonie circuit, and also provided with means for collecting and conveying to the ear of the listener sound-waves directly produced.

The same letters of reference indicate like parts in the several tigures in which they occur.

Ais a reflectingphotophonic transmitter; B, the intermittent-beam apparatus; C the photophonic receiver; D, a galvanic circuit; E, an ordinary hand-telephone; F, an induction-coil.

The retiecting-transmitter A consists of a mirror of thin silvered glass,a, which is thrown into vibrations by the voice of a person speaking into the tube a', and retlects more or less of the beam of sunlight or other radiant beam toward the receiver C.

The intermittentbeam apparatus B comprises two disk-wheels, b, with a series of radial openings in the path of the beam. One of these disk-wheels is stationary and the other revolves, or they both revolve in opposite directions, or in the same direction at unequal velocities. The beam, being consequently cut ott by the blank spaces and allowed to pass through the openings when those in one disk register with those in the other, is intermittent in its action. A beam from the still or from an artificial source can be employed with this apparatus. The beam can be concentrated before or after passing through the disk-wheels, and can be reccted by mirrors to the proper path, or allowed to fall directly upon the wheels.

These two forms of transmitting apparatus are shown as types. Any photophonic tra-nslnitter ofordinary or suitable construction can be used with the improved receiver.

In Fig. l the receiver C consists of a funnelshaped sound-chamber, c, the interior flaring walls of which are smoked or covered with a deposit ot' lamp-black, rlhe mouth is covered with a glass plate, c', and a sound-conveying tube, c2, communicates with the contracted portion in the rear. Speech or other sound uttered into the tube a ofthe transmitterA can be heard by listening at the tube c2 ot' the receiver C. The distance over which speech can be transmitted in this wayand the distinctness ot' the sounds reproduced depend upon the energy ofthe beam employed.

ln Fig. 2 the receiver C contains a piece of wire-gauze, c3, upon which the lam p-black :vis deposited. 'lhe walls of the sound-chamber@ can also be smoked, as shown, or not, as desired. The sound is received by the tube c2, as before.

In Figs. 3 and 4the receiver is alamp-black cell, and comprises the glass plate or insulating support d, the intermeshing combs or conductors ee', of silver film, the binding-postsf j", connected with the conductorse e, respectively, bythe metallic plates gg', and the lampblack x.

In forming the cell the silver is deposited in any ordinary or suitable way. The desired 'portions are removed or scraped oit' by means ot" a tool with a fiat end. This tool can be made like a chisel, or a punch with conical point can be ground off or cut at right angles to the axis, so as to leave a tlat end with a diameter equal to the desired width of the stripe to be removed. The mechanical ruling or scraping of the plate can be easily effected by means of an ordinary lathe provided with a slide-rest. The tool is held in a frame supported between centers. The plate is clamped to a bed-plate beneath with the silvered side uppermost, in such position that when the tool is pressed down and penetrates the film its operating end rest-s tlat upon the surface of the glass. The bedplate carrying the silvered plate can be worked lengthwise of the lathe to rule or scrape ot' the lines in one direction, and then moved across at right angles to the length to bring the plate into position for scraping a new line.

It is not necessary to remove the tool from the plate. The lengthwise movement under the tool removes the film so as to form the spaces between the teeth of the combs, and the transverse movementconnects these spaces with each other alternately at opposite ends.

The binding-posts are fastened to the glass plate in any ordinary or suitable way, and are in electrical connection with the two parts ot' the conducting-film. 'lo apply the carbon the silvered side ot' the glass plate is smoked over a suitable burner.

In Fig. the silver film is scraped o'in thc form ot' a double spiral, leaving the conductors c e. In Fig. (iv the conductors e c have curved intermeshing teeth. In these gures the lamp-black :r is shown as confined to the spaces between the conductors in order to show the latter more clearly; but in practice the conductors would ordinarily be themselves coated.

In Fig. 7 the poles of the galvanic circuit D are connected with the binding-postsfj". A musical note produced by the action of the intermittent beam can be heard by applying the. telephone E to the ear.

In Fig. 8 the lamp/-black cell is placed in a sound-chamber, c, and is connected with a battery in the primary circuit ot the inductioncoil F, the telephone-E being connected in the secondary circuit of the coil. The chamber C has a glass plate, as in Fig. 1, through which the radiant energy is transmitted, and a hearing-tube, c2, for conveying the sound-waves produced in the receiver to the ear. Sounds uttered into the tube a of the transmitter can be heard either by listening at the tube c2 or by means ot' the telephone E.

It is obvious that various modifications may be made wit-hout departing from the spirit of the invention, and that parts of said invention could be used without the others. The forms of cells used for selenium can be used with lamp-black, and the improved cell can be ein ICO IIO

ployed with any suitable form of sensitive medium; but the metal composing the conductors should be such as not to be injuriously affected by the action of the sensitive medium.

rlhe insulating-plate with the ruled or scraped silver tilm thereon can be employed to measure the electric conductivity of various substances, liquids, and gases by connecting the binding-posts with the poles ot a galvanometer-circuit and immersing the plate With the substance to be tested, or covering the silvered side with the same. In some cases the silver film can be deposited on both sides of the plate and ruled as before described.

Telephonie transmitters and receivers can be formed by means ot' apparatus like the lampblack cell; but these will form the subject of separate applications.

That part of the invention which relates to the conversion of the radiant vibrations into electrical vibrations is not limited to lampblack, but includes other forms of carbon, and also other materials which operate in a substantially similar manner to lamp-black.

Having now fully described our said invention and the manner of carrying the same into effect, what we claim is 1. In a photophonic receiver, the soundchamber for containing the sensitive medium, having a wall transparent to light or radiant energy, but opaque orless transparent to sound, substantially as described.

y2. The combination of the sound-chamber, having a wall transparent to radiant energy, but opaque or less transparent to sound, with the sensitive medium therein contained, and a sound conveyer or opening communicating with the interior of said chamber, substantially as described.

3. In a photophonic receiver, the sensitive medium, composed of vibratory material in an open, porous, or subdivided condition, substantially as described.

4. In aphotophonic receiver,a sensitive medium of lamp-black or similar material, substantially as described.

5. Aphotophonic receiver having as the sensitive medium a deposit of vibratory material in a loose, porous, subdivided, occulent, or spon gy condition, substantially as described.

6. In a phctophonic receiver, the combination of a sensitive medium conductive of electricity, in a loose, porous,'or subdivided condition such as lamp-black, and conductors for including the same in au electric circuit, substantially as described, so that radiant vibrations can be thereby converted into electric vibrations, as set forth.

7. rJhe combination ofthe lamp-black or other vibratory conducting material in loose particles, the rigid or substantiallyinextensible support of insulating material, and conductors by which the lamp-black can be included in an electric circuit, as set forth.

8. AcellA comprising sheets, plates, or strips of conducting material, fixed or mounted upon a support of insulating material, with their edges opposite each other and separated by a suitable distance, and sensitive conducting material in the space or spaces between said edges, substantially as described.

9. A support of insulating material, having comb-shaped conductors fixed or mounted on said support, as indicated, so that the teeth of the combs intermesh but are not in contact With each other, substantially as described.

10. A silvered plate having the silver film mechanically ruled or scraped, as described, so as to leave parallel lines or stripes of equal width,and with sharp,clean ed ges,substantially as set forth.

11. The insulating-plate having on one or both sides a silver film ruled or scraped, as described, so as to divide the silver iilm into two or more conductors, in combination with bindin g-posts connected with the parts of said film or films, substantially as set forth.

12. The combination of the insulating-plate and ruled silver film with the lamp-black or sensitive medium included in the ruled or scraped spaces in said tilm, substantially as set forth.

13. The combination, with a galvauic circuit, ot' a photophonic cell comprising a glass plate with ruled silver film thereon, lampblack deposited in the ruled spaces in said lm, and connections for completing the galvanic circuit through said cell, substantially as described.

14. rIlle combination, with a photophonic cell, of an induction-coil, electric connections for including said cell in one circuit of said coil, and a teleph one-circuitconnected with the other circuit of said coil, substantially as described.

15. A Vphotophonic receiver comprising a sound-chamber having a wall transparent to radiant energy, but opaque or less transparent to sound, a cell having a vibratory sensitive medium, such as lamp-black, electrical connections for connecting said cell in an electrical circuit, and a hearing-tube connected with` the interior of said sound-chamber, substantially as described.

In testimony whereof we have signed this specification in the presence of two subscribing witnesses.

ALEXANDER GRAHAM BELL. SUMNER TAIN'IER. Witnesses:

FHILIP MAURO, A. PoLLoK.

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